The TrkB–STAT3–miR-204-5p regulatory circuit in endometrial cancer. Left: In normal cells, a recurrent auto-regulatory circuit involving the expression of TrkB induces phosphorylation of STAT3 to negatively regulate the expression of miR-204-5p. MiR-204-5p, in turn, represses TrkB expression. The expression of miR-204 within this circuit maintains endometrial cells in a normal differentiated state. Right: In endometrial cancer cells, this circuit becomes dysregulated due to increased activity of the TrkB–STAT3 component of the circuit, which constitutively represses miR-204-5p. In the absence of sufficient miR-204 tumor suppressor activity, TrkB is left uncontrolled, thereby leading to carcinogenesis.